1. Field of the Invention
The present invention relates to an optical pickup device, and more particularly to an optical pickup device for recording/reproducing with respect to a recording medium having laminated recording layers.
2. Disclosure of Related Art
In recent years, the capacity of an optical disc has been increased. An increase in the capacity of an optical disc is realized by forming a plurality of recording layers in the disc. For instance, there has been commercialized a multilayer disc having two recording layers on one surface thereof, such as a DVD (Digital Versatile Disc) or a Blu-ray disc. An optical disc having three or more recording layers is advantageous in further increasing the capacity thereof.
However, forming a plurality of recording layers in a disc has a problem that reflection light from a recording layer other than a targeted recording layer to be reproduced may be entered into a photodetector, with the result that a reproduction signal may be deteriorated. This problem is known as a so-called interlayer crosstalk resulting from stray light. Accordingly, it is necessary to provide an arrangement for smoothly suppressing/removing stray light, in the case where a plurality of recording layers are formed in a disc.
As a method for removing stray light, for instance, there is proposed a method, wherein a pinhole is formed in front of a photodetector. As other methods for removing stray light, there are proposed a method, wherein a forward light blocking plate and a rearward light blocking plate are disposed in front of a photodetector, and a method using a polarized optical element.
However, in the method, wherein a pinhole is formed in front of a photodetector, stray light as well as reflection light from a targeted recording layer to be reproduced may reach to the photodetector through the pinhole . In this method, there is a problem that a small distance between recording layers may increase the amount of stray light passing through the pinhole, which obstructs proper removal of interlayer crosstalk. The method, wherein a forward light blocking plate and a rearward light blocking plate are disposed, has a problem that the use efficiency of reflection light may be lowered to about 50%, because a half of the reflection light from a targeted recording layer to be reproduced is blocked. In the method using a polarized optical element, many optical components for removing stray light are required, which causes an increase in the cost.